Method of adding fire retardant chemicals to a fiber board while on the forming wire



Sept. 6, 6 R. H. BESCHER METHOD OF ADDING FIRE RETARDANT CHEMICALS To A FIBER BOARD WHILE ON THE FORMING WIRE 2 Sheets-Sheet 1 Filed June 5, 1964 STOCK ..17 42 IZOI7L P255555 WATER CHEST o 2 e5 v I rovraonmr ua mAcHnlrr 2 0 0 -18 .35 Z l MAJOR PORTION or mm: Lnwoz i STOIEAGL CHLMICAL MAKE-UP INVENTOR.

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327L238 Patented Sept. 6, 1966 METHOD F ADDING FIRE RETARDANT CHEM- ICALS TO A FIBER BOARD WHILE ON THE FORMING WIRE Ralph H Bescher, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed June 3, 1964, Ser. No. 372,353 2 Claims. (Cl. 162-159) This invention relates to the production of articles, such as ceiling tile, from separated cellulosic fibers such as wood fibers, and more particularly, to a process whereby the articles will be rendered fire resistant and as such is a continuation-in-part of my copending application Serial No. 108,047 filed May 5, 1961, and now abandoed.

Processes for the production of molded articles such as ceiling tile, semi-hardboard, hardboard, and the like from cellulosic fibers, are well known. =Wood fibers and fiber bundles for the conventional fabrication of hardboard, for example, fall into a receiver and are carried by water (known as white water) to la Fourdrinier machine where the fibers become entwinded and entangled on a moving wire belt and are formed as a thick, continuous, fibrous mat or layer. Water is drained from the mat through suction on the Fourdrinier machine and excess water is thereafter removed by passing the mat through sequencing rolls. This thick mat is then cut into pieces of desired size and dried by subjection to high pressures and temperatures for a sustained period of time in drying cylinders or in hot presses and the like.

Boards as produced above are widely used in the construction of structures, for example, in the building of houses. Such products are. of substantial thickness. Acoustical ceiling tile, for example, may be from one-half to one inch in thickness, twelve inches in width and from twelve to more than twenty-four inches in length. It would be desirable, therefore, that the boards be fire resistant, insect resistant, fungi resistant, etc., but since the boards are made of wood, they are readily burned and attacked by insects and fungi.

It has been suggested heretofore to subject relatively thin materials, such as, paper, to a fine spray of solution to impart to the paper characteristics such as glassine, water resistance, grease resistance, and parchment-like qualities. Even then, as described, for example, in Patent No. 2,112,540, special precautions must be taken to spray the solution in the direction of travel of the Fourdrinier machine to prevent disturbance of the wood fibers that constitute the film of paper.

It has now been found that fire resistance and other desirable characteristics may be imparted to relatively thick mat board of Wood fibers by removing a major portion of the white water from the mat that is formed of the wood fibers, thereafter flooding the top of the mat with a concentrated solution of chemicals that impart fire-retardant properties thereto, drawing this solution through the mat by suction, recovering the latter solution that was pulled through the mat, and recirculating the recovered solution for reuse in the flooding of mats, the concentration of chemicals in the recovered solution being maintained at a desirable level by further addition of the desired chemicals thereto.

The foregoing and other novel features and advantages of this invention will appear more fully from the detailed description which follows when taken in conjunction with the accompanying drawing. It is to be understood, however, that the drawing is for the purpose of illustration only and is not to be construed as a limitation on the invention.

FIGURE 1 illustrates schematically the apparatus for carrying out the invention.

FIGURE 2 is a detailed view of the Fourdrinier machine as modified to carry out the invention.

FIGURE 3 is a graph reflecting the fire-retardant characteristics of fiber boards treated in accordance with the process of this invention.

A conventional Fourdrinier machine, in accordance with this invention, is readily modified so as to carry out the steps of the invention.

Referrng now to FIG. 1, the conventional apparatus for producing board from wood fibers comprises stock chest 12, Fourdrinier machine 13, and presses 24 and 25. Drying means other than a hot press may be used without departing from the process of this invention.

The fiber and bundles fall to a stock chest 12 and are carried by water, i.e. white water, to the Fourdrinier machine 13.

Fourdrinier machine 13 may be of a conventional type. A traveling wire screen or cloth 15 is supported by two rows of bearings 17 and 18 in such a way that a portion of the screen receives the wet wood fibers from stock chest 12, and travels it forwardly in a horizontal or nearly horizontal plane but may additionally be given a sidewise motion or shake. Such motion effects an intertwining of the fibers upon the surface of screen 15. The Water which suspended the fibers drains, in part, through the screen due to gravity. Gravity flow at this point permits the necessary felting of the fibers. The wet sheet passes through squeezing rolls, not shown, which remove the majority of the white water. Since the white water that is used to convey the wood particles from chest 12 to the Fourdrinier machine 13 dissolves wood sugars and other water-soluble extractives from the wood, this white water is discarded. Suction boxes, not shown, are on the underside of the screen 15. The fibers thus form a mat on the screen and by the time a portion of the mat reaches the forward end, if sufficient water has been removed from the mat, the mat can support its own weight.

By means of felt blankets, the mat is fed through a series of roll-type presses that remove additional Water from the sheet and compact the mat. The thick, wet mat is trimmed and cut to pieces of desired size by cutters, not shown. To make hardboard, the individual pieces are fed to a hot press 25 where the mats are compressed for a period of time, usually about 8 to 20 minutes at a high pressure, for example, 1,000 psi, and at a high temperature, for example, 350 F. The finished board is then removed from the press.

The foregoing has described a conventional process for the production of wood hardboard, semi-hardboard and other pressed molded articles from cellulosic fibers.

In accordance with this invention, after the action of gravity and squeeze rolls has removed a major portion of the white water from the mat on the Fourdrinier machine, the mat is then flooded with a concentrated solution of chemicals that will impart a desired characteristic to the wood; this solution is drawn through the fibers by a vacuum, and the solution is recovered for reuse in flooding the mat on the machine so that the process is continuous. Additional chemicals may be added to the solution so as to maintain the necessary concentration of solution.

By flooding is meant the addition of sufiicient liquid so that a pool forms on the surface of the mat. The pool will usually be of about one-half inch in depth on the mat. Surprisingly, the pool or flood of water does not appreciably distentwine the fibers. The flooding of the mat in this manner provides suificient chemical composition to replace at least an equal weight of water that was contained in the wet board. This volume of solution will conventionally be from two to four pounds of water per pound of dry fiber. There remains in the mat fire retardant chemicals that had been carried in the solution to the extent of 15 of the dry weight of the board.

By major proportion of white water is meant removing from 90% to 95% of the free water that is contained in the slurry fed to the Fourdrinier machine from the stock chest and that is removed in the Fourdrinier machine.

To permit flooding in accordance with this invention, the Fourdrinier machine described above is modified as follows:

In FIG. 2 concentrated chemicals are introduced by a line 1 to a flood box 3 mounted above the Fourdrinier machine 13. The box overflows the solution through distribution slots 4 across the moving mat 15, and the solution is about one-half inch in depth on the mat. The excess solution drains through that mat into the suction boxes 21 located at a further position further forward in the line of travel of the mat than the suction boxes that are used to take up the white water. From the suction box 21, the recovered fire-retardant solution is passed by line 22 to a separating tank 23. Liquids enter the separating tank at an intermediate level. Air and other gases escape from the liquids and are exhausted overhead through a line 30 by means of a vacuum pump 31 which discharges the gas to the atmosphere and at the same time draws the suction from the suction boxes 21. From the bottom of the separating tank the liquid is pumped away through line 37 by means of pump 33. The fire-retardant solution line 37 leads to the make-up storage tank 36 to which fresh chemicals are added to make up for those deposited in the mat. From the storage tank, the make-up liquor with the added fresh concentrated solution is recycled back to the flood box.

Concentrated solution which is to be flooded on the mat may be made by dissolving a composition of salts comprised of by weight 45% ammonium hydrogen phosphate, 45% of ammonium sulfate, and of sodium fluoride in water so that the solution contains from 5% to 50% by weight of this composition. Other fire-retardant chemicals, such as ammonium sulfate, ammonium phosphate, dicyandiamide phosphoric acid, borax, boric acid and zinc chloride may be used as the fire-retardant solution without departing from the invention.

When the concentrated solution is then pulled through the mat, a necessary amount of the salts remain in the wood, and some of the original white water is also removed from the concentrated solution; to maintain this solution at its advantageous concentration, new salt solution is added to the recovered solution to replace equally the weight of salt solution remaining in the fiber board. The amount of white water removed with the concentrated solution does not have to be discarded in the same manner as in the original white water which was removed. The quantity of white water removed from the boards and replaced by the water containing the concentrated fire-retardant solution is very minimal. As the concentration of impurities increases in the recovered solution, they will be replaced in the board along with the fire-retardant chemicals and a balance is reached. The small amount remaining in the board at the time it reaches the suction boxes could be allowed to remain in the board without changing its physical characteristics and, if the water is recirculated without loss, this will result. Therefore, there will never be any greater amount of impurities in the board than originally remained after removal of the major portion of white water.

A fiber board ceiling tile made in accordance with the invention was found to contain 10% by weight of the composition of fire-retardant salts. The board, when tested according to fire tube A.S.T.M. Test No. E69-50, showed a weight loss of only 30%. It has been found that the wood should contain from 5% to 15% of fireretardant salt to show fire-retardant characteristics. It is preferred that the wood contain 10% by weight of fireretardant salt. If the board contains less than 5% by weight of the salt, the desired fire-retardant characteristics according to fire tube test A.S.T.M. No. 1369-50, as shown in FIG. 3 of the drawings, are not sufficient. If the amount of fire-retardant salt contained in the fiber board be greater than 15 the fire-retardant characteristics of the board do not spectacularly increase, although obviously a gradual increase will be observed the greater the amount of fire-retardant salt used. The graph, as shown in FIG. 3 of the drawings, illustrates the curve by which fire-retardant characteristics of treated fiber board have been determined. It can be seen that as the amount of fire-retardant salt is increased above 15%, the fireretardant characteristics of the board do not proportionately increase.

It will be readily understood that numerous modifications may be made in the above illustrative description without departing from the spirit of this invention. The impregnating agent used and its concentration will depend, of course, upon the characteristics which it is desired to impart to the fiber board. The foregoing has described imparting fire-retardant characteristics to a product such as ceiling tile that is made from wood fiber. To impart preservative characteristics to the fiber board so as to make the board repellent or toxic to organisms that would otherwise attack it, the mat is flooded with a solution of a water-soluble preservative. For example, a composi tion comprised of a solution of sodium fluoride can readily be impregnated into the fiber board to provide a preservative contained in the board equal to 23% of the weight of the mat. The preservative solution is not limited to sodium fluoride but rather can include other compounds, such as aluminum sulfate, copper arsenate, copper sulfate, mercuric chloride, nickel chloride, sodium chromate, sodium dichromate, zinc acetate, zinc sulfate, sodium pentachlorphenolate, and the like.

It will also be understood that the scheme of operation illustrated in the accompanying drawing may be varied without departing from the scope of the invention. Instead of the flood box, as illustrated in the drawing, from which the preservative or fire-retardant solution overflows onto the mat, any other container capable of spreading the solution over the mat so as to cover the entire area of the mat may be used. It will also be readily apparent that compounds already known and useful for imparting desirable characteristics to wood can be used effectively with the apparatus and process hereinabove described.

The foregoing has described the novel process for imparting desired characteristics to board made from wood fibers without experiencing a great economic loss of chemicals and without the use of substantial additional water which would have to be dried from the boards. The novel process requires only a minor capital expenditure and no additional heat or labor.

I claim:

ll. Process for the production of a fire retardant artificial board that is made from wood fibers which comprises:

conveying a suspension of wood fibers in water onto a moving wire belt, removing by suction a major portion of said water from said wood fibers so that the wood fibers become entangled to form a continuous layer,

thereafter flooding said layer with a concentrated aqueous solution of fire retardant chemicals so that a pool about one-half inch deep of said solution and being about 2 to 4 pounds of water per pound of dry fiber forms on said layer,

5 6 drawing said solution through said layer by suction References Cited by the Examiner so that said wood fibers retain an amount of about 5% to 15% by weight of said fire retardant chem- UNITED STATES PATENTS icals to become fire retardant, and 1,996,832 4/1935 Rosmait 162-266 recovering said concentrated solution so passed through 5 2 112 540 3/1938 McAndrews et a1. 162 136 said layer for use for flooding additional layers of said wood fibers. FOREIGN PATENTS 2. The process of claim 1 wherein said concentrated aqueous solution comprises 5% to 50% by weight of 69O434 4/1953 Great Bntam' a mixture whose composition on a weight basis is about 10 45% ammonium hydrogen phosphate, about 45% am- DONALL SYLVESTER P'lmary Examme" monium sulfate, and about 10% sodium fluoride. BASHORE, Assistant Examiner 

1. PROCESS FOR THE PRODUCTION OF A FIRE RETARDANT ARTIFICAL BOARD THAT IS MADE FROM WOOD FIBERS WHICH COMPRISES: CONVEYING A SUSPENSION OF WOOD FIBERS IN WATER ONTO A MOVING WIRE BELT, REMOVING BY SUCTION A MAJOR PORTION OF SAID WATER FROM SAID WOOD FIBERS SO THAT THE WOOD FIBERS BECOME ENTANGLED TO FORM A CONTINUOUS LAYER, THEREAFTER FLOODING SAID LAAYER WITH A CONCENTRATED AQUEOUS SOLUTION OF FIRE RETARDANT CHEMICALS SO THAT A POOL ABOUT ONE-HALF INCH DEEP OF SAID SOLUTION AND BEING ABOUT 2 TO 4 POUNDS OF WATER PER POUND OD DRY FIBER FORMS ON SAID LAYER, DRAWING SAID SOLUTION THROUGH SAID LAYER BY SUCTION SO THAT SAID WOOD FIBERS RETAIN AN AMOUNT OF ABOUT 5% TO 15% BY WEIGHT OF SAID FIRE RETARDAANT CHEMICALS TO BECOME FIRE RETARDANT, AND RECOVERING SAID CONCENTRATED SOLUTION SO PASSED THROUGH SAID LAYER FOR USE FOR FLOODING ADDITIONAL LAYERS OF SAID WOOD FIBERS. 